US3685784A

US3685784A - Injection mold wherein moveable cavity portions act to close the mold gates and further compress the mold material

Info

Publication number: US3685784A
Application number: US878104A
Authority: US
Inventors: Keith Gordon Spanjer
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1969-11-19
Filing date: 1969-11-19
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22
Also published as: DE2056927A1; JPS503099B1; NL7016596A; DE2056927C2

Abstract

A method of molding and a mold are provided for encapsulating devices such as axial lead cylindrical electrical devices in which two separable portions of the mold closely embrace the axial leads near the axial ends of the mold cavity and one of the mold portions includes piston-like parts, one for each molding cavity, which moves between at least two positions. In one position of a piston-like part of the mold, and mold cavity is open to receive encapsulating fluid and in the other position of the part the mold cavity is completely closed. In a modification, the piston-like parts are each shaped and positioned to form parts of adjacent molding cavities. The molding process involves supplying encapsulating fluid to the several cavities by applying pressure to the whole body of fluid and applying higher pressure to the fluid in each molding cavity.

Description

United States Patent Spanjer [451 Aug. 22, 1972 54] INJECTION MOLD WHEREIN 2,380,084 10/1945 Strauss 1 8/16 F MOVEABLE CAVITY PORTIONS ACT 2,913,767 11/1959 Simon 18/30 WR TO CLOSE THE MOLD GATES AND 3,268,960 8/196 Morton ..18/3O WR Inventor:

FURTHER COMPRESS THE MOLD MATERIAL Keith Gordon Spaniel, Scottsdale, Ariz.

Assignee: Motorola, Inc., Franklin Park, Ill.

Filed: Nov. 19, 1969 Appl. No.: 878,104

425/250, 425/443 Int. Cl ..B29c 1/00 Field of Search..l8/3O PT, 30 WC, 36, DIG. l0,

I8/DIG. 38, I D, 2 RM, 2 RP, 2TP, 16 F, 42'. D, 5 E, 42 J, 30 WM, 30 WR, 30 PM;

References Cited UNITED STATES PATENTS 9/1970 Burns ..249/97 X Primary Examiner l. Spencer Overholser Assistant Examiner-David S. Safran Attorney Mueller and Aichele ABSTRACT A method of molding and a mold are provided for encapsulating devices such as axial lead cylindrical electrical devices in which two separable portions of the mold closely embrace the axial leads near the axial ends of the moldcavity and one ofthe mold portions includes piston-like'parts, one for each molding cavity,

3 Claims, 8 Drawing figures PATENTEDnuszz I972 SHEET 2 [IF 3 Q2 @Q m Keith Gordon Spanjer m wd MA ATTY'S.

PATENTEDwszz 1972 3,685,784

saw a or 3 Fig. 8

I INVENTOR.

Keith Gordon Spanjer BY M M 9* ATTY'S.

INJECTION MOLD WHEREIN MOVEABLE CAVITY PORTIONS ACT TO CLOSE THE MOLD GATES AND FURTHER COMPRESS THE MOLD MATERIAL BACKGROUND In the prior art method of encapsulating a device, two mold portions are provided which, when put together in a proper manner, form a molding cavity. The article to be encapsulated is placed in the cavity and encapsulatingfluid is fed under pressure into the cavity by way of the small passageway called a gate in either one of the portions of the mold or partly in both portions of the mold. A connecting tube or runner is provided connecting the central container for the molding fluid to the several gates. Since the gate area is small in comparison to the cross-sectional area of the cavity, the velocity of flow of encapsulating fluid is high, whereby the device to be encapsulated may be damaged by the flow. The fluid hardens and the mold parts are separated and the encapsulated item is taken out of the mold, usually by hand. The gate material as well as the material in the runner is wasted. Also, the gate material must be broken off the capsule leaving a rough spot that may interfere with labelling the capsule, especially if the capsule is small, whereby it may be necessary to smooth the surface of the article before it can be sold. Furthermore, if the capsule has axial leads, the encapsulating material may contact the leads for an undesirable distance along the length thereof, whereby the material must be cleaned off of the leads. Such cleaning and smoothing operations are difficult and expensive. In addition, in the prior art,'since pressure is applied to the molding liquid at a distance from the mold cavity, the mold cavity may not be full, or, if full, all parts of the molding material may not have the same pressure applied thereto. Therefore, the molded articles as provided by the prior art method and mold may have differing densities in different portions thereof.

It is an object of this invention to provide an improved method of molding.

It is an object of this invention to provide an improved mold.

It is another object of this invention to provide a method of molding and a molding apparatus in which the amount of waste of molding material is minimized, the molding material is kept off the leads to the completed capsule, and closeable gate is provided, and the density of the molding material of the encapsulated package is unifonn throughout the volume thereof.

SUMMARY In accordance with the method of this invention, the encapsulating fluid is fed to molding cavities through large gates, which can be opened and closed, under centralized pressure, and as the gate is closed localized pressure is applied to the fluid in each cavity. When the fluid has hardened, the capsule is ejected from the cavity. Further in accordance with this invention, a mold is provided having an upper and a lower portion, which when fitted together provide a cavity of the shape of the finished encapsulated article or capsule. The lower portion includes at least one piston-like part for each cavity which is moveable with respect to the lower portion. When a piston is in one of its extreme positions, a

passageway is provided along the length of the mold are formed in the mold portions with encapsulating fluid. The passageway is so large that the flow of fluid into the cavities is slow, whereby the article to be encapsulated is not damaged by fluid flow. When the piston is in an intermediate position, the cavity takes the shape of the finished capsule and the feeding gate is cut ofi.

In the process of moving the piston to its intermediate position, the encapsulating fluid is compressed into the mold cavity, whereby the density of the capsule is made-uniform. Since the feed gate is cut off when the piston arrives at its intermediate position, there is no gate material whereby waste of encapsulating material is reduced and the surface of the capsule is smooth. The fluid is fed from cavity to cavity along the length of the mold whereby the passageway for the fluid is shortened, further saving encapsulating fluid. If the capsule has leads, the upper and lower portions of the mold are tightly clamped on the leads at the ends of the cavity before the fluid is forced into the cavity, whereby no or very little encapsulating fluid comes into contact with the leads, whereby cleaning the leads is avoided. After the fluid is hardened, the piston is moved to its other extreme or to an ejecting position to eject the finished The invention will be better understood upon reading the following description in connection with the accompanying drawing in which:

FIG. 1 is an exploded vertical section of a mold according to this invention for providing a cylindrical capsule having axial leads and showing the relative position of the mold portions and the finished capsule,

FIG. 2 is an exploded vertical section of the mold of FIG. 1 taken, however, at from the section of- FIG. 1, and also showing the relative position of the mold portions to the finished capsule,

FIG. 3 is a top view of the lower portion of the mold of FIGS. 1 and 2,

FIGS. 4 and 5 are sectional views of the mold portions that are useful in explaining the inventive method and the operation of the mold of FIGS. 1-3,

FIGS.'6 and 7 are, respectively, vertical section and a plan view of a modified mold of this invention, and

FIG. 8 is a top view of a molding machine using the described molds and showing how the encapsulating fluid is fed to the mold cavity.

In general, in accordance with the prior art, encapsulating material is bought in a granular form; a certain amount thereof is weighed out and heated until it becomes a pliable mass which is called a pill. The pill'is put into a reservoir such as reservoir 10 of FIG. 8. The articles 15 to be encapsulated are placed in the mold cavities in the lower half of the molds and the upper half of the molds is put over the article, and the two halves of the molds are fixed together. To assist in feeding the molding machine of FIG. 8, the supports 9 are loaded with articles 15, whereby a great many articles 15 may be placed in respective molding cavities of the lower half of the molds 13 at the same time. The pill is melted and the fluid is put under pressure of about I 3. 3000 pounds per square inch by piston means 11 contained in the reservoir 10. The fluid runs along

passageways

12,12 to the molds 13. Centralized pressure is applied by pressure means 11 in the central reservoir to theliquid, and passageways, not shown JinFIG. 8, are provided along the molds and individual gates are provided between the passageways and the in- FIG. 8,four molds 13, each comprising a plurality such as 50 molding cavities, may be supplied with the articles to be encapsulated and with encapsulation fluid at the same time, whereby about 200 encapsulated articles are made at one time. When it is judged that all the molds are full, the fluid isallowed to cool down and whatever material is'left in the reservoir 10, called the cull, and the materialin the passageway or runners 12 dividual cavities formed by the molds. As is shown in centrally formed with a semi-cylindrical cavity 42 that in the passageways extending along the length of v the individual molds'and the gates (not shown) are thrown away. The molds are taken apart'to take out .20 manually the finished articles that have the gate material attachedthereto and the gate material ,is broken off and the articles are polished if necessary. If the article has leads, often the leads have molding material stuck i thereto sofar beyond the end of the capsule as torequire cleaning the leads. Frequently, the cavities in the molds that are at extreme distance from the reservoir 10 or those 'cavitiesfto which the passageway ,or the gate holes has not been carefully cleaned out are not filled with encapsulating fluid, whereby the encapsulation of. the article l5v is not perfect. The pressure in encapsulate articles having axial leads. The articles 15 (shown-in FIG. 8) .to be encapsulated may include a central rectifying junction and coaxial leads 18. The finished articles 14, shown in. FIGS. 1 and 2,-have a cylindrical "body portion 16 fully encapsulating the rectifying junction and axial leads 18 extending from the body portion 16.

First, considering FIGS. 1, 2, and 3, the upper portion 20 of a mold embodying the structural aspects of the invention and with which the method of this invention can be practiced has a semi-cylindrical cavity 22 which fits one-half of the circular surface and one-half of each end surface of the cylinder 16. The

groove portions

24,24 of the upper moldportion are adjacent the semi-eylindrical portion 22 thereof and fit the upper halfof the leads 18 for a short portion of their length.

Longitudinal grooves 26 are provided in the lower face of the mold portion 20 beyond the lead fitting grooves 2410 provide clearance for leakage of encapsulating fluid-( if any) out of the cavity 22 along the leads l8. Portions 28 of the upper lead portion 20 and beyond the grooves 26 push the leads 18 down in the comb'part 30" of the lowerportion 32 of the. mold as will be described.

I The lower portion of the mold of FIGS. 1, 2, and 3 in- I cludes the outer comb part30 having lower semi-cylindrical grooves 34 for receiving the lower part of the leads 18. Longitudinal grooves 36 which match with grooves 26 are next in the inwardly direction from the combs 30. Grooves 38 are provided tofit the lower part of the leads 18 adjacent the cavity for forming the cylindrical portion 16 of the article 14. As will be made more clear, when the upper portion 20 and thelower portion 32 abut each other, the

portions

24 and 38 so closely fit the

leads

18,18 that fluid does not leak out, or very little fluid leaks out, along' the

leads

18,18.

The bottom of the lower mold portion 32 is provided I with a vertically moveable piston-like part or slider 40. The top of the piston'40, as shown in FIGS. 2 and 3, is

fits the lower portion of the cylinder 16. The top of the piston 40, on both sides. of the cavity 42, is flat, as

shown at 44, FIGS. 2. The'center of the lower portion 32 of the mold between the sides, of the .pistons40 forrns'flat surfaces 46 which are below, by about twenty thousandths of aninch, the-upper or longitudinally-extending spaced parallel surfaces 48 which extend between the grooves on each side of the cavity The piston 40 is moveable between its lowest position as shown inFIGS. 2 and 4 in which the surfaces44 are 1 flush with the surfaces'46 and its intermediate position shown in FIG. 5.in which the surfaces 44 are flush with the surfaces 48 and are in tight contact with the surface Q '50 of the upper mold'portion20. When the surface 44 is flush with the surface 46, and when the

mold portions

20 and 32 are clamped together, leads such as the leads 18 are tightly clamped in'semi-cylindrical grooves 24 I and 38 which together'closely embrace the leads 18', the surfaces 48 closely embrace the leads 18, and the surfaces 48 closely contact the corresponding portions of the surface of the mold portion 20 between the cavities 22. However, there is a large space I or passageway 99 (see FIG. 4) between the surface 46 and the corresponding portion of the surface 50 and also between the upper surface 44 and the corresponding portion of the the surface 50 for flow of fluid from one end of the mold, comprising the two

mold portions

20 and 32, to the other end thereof. This is shown inFIG. 4 in which the passageway 99 isprovided along the whole length of the mold between the surface 50 and. the cavity22 of the upper mold portion 20and the intermediate surface 46 of the bottom mold portion 32 '1 and the upper surface 44 and upper cavitysurface 42 of the pistons 44. However, the surface48 of the lower and the surface 50 of the upper portion 20, including portion 42, including the semi-cylindrical portions 38,

the semi-cylindrical portion 24, contact each other at each end of

cavity portions

22 and 42 or they embrace the leads-l8, whereby fluids can come in through the passageway 99 as described but cannot leak out. The

passageway 99 -is as wide as the

cylindrical cavity

22 and 42 is long and is about twenty thousandths of an inch deep. Thearea of the passageway is made'large, about 20 percent of the cross-sectional area of the finished article 14, whereby flow of fluid into the than if a small gate of several molding cavities is slower the prior art were used.

In the use of the mold of this invention, the lower j portion 32 of the mold with the pistons 40 in their lower position (and with the upper portion of .themold 20 out of theway) is loaded in a known manner with rectifiers 15 (for example) to be encapsulated. Then the upper portion 20 of the mold is properly placed on the lower portion 32 and these two

portions

20 and 32 are clamped together in a known manner, the pistons 40 being in their lower position. Then encapsulating fluid from the reservoir is fed to the passageway 99 of the completed mold, the fluid running in a direction of the arrows 100 in FIG. 8 into and through successive cavities. When, due to the pressure in the pot 10 as provided by the pressure providing means 11, all the cavities formed by the mold portions and 32 are filled, the cam means 60 is moved in such a direction, to the right as viewed in FIGS. 4 and 5, as to raise all the pistons 40 simultaneously until they take the position shown in FIG. 5 in which the top surface 44 of each piston 40 is flush with and contacts the surface 50 of the upper mold portion 20. The passageway 99 is tending surfaces 48 which abut the surface 50 of the upper mold portion longitudinally and at each side of the cavities that are formed by the upper cavity portions 22 and the lower cavity portions, to be described.

The lower mold portion 100 is formed with fixed bridge portions 102 that are in central registry with the cavity portions 22 when the

mold portions

20 and 100 are properly assembled. The tops of the fixed portions 102 have partly cylindrical cavities 104 formed therein, the cavities 104 forming part of the same cylindrical cavity that fits the cylindrical portion 16 of article 14 of FIG. 1. A piston 106 is provided between each two greatly reduced in length because several portions thereof are cut off between the several pistons 40. The semi-cylindrical surfaces 42 and 22 form cylindrical cavities which are concentric with the leads, 18,18 which are embraced by the

semi-cylindrical grooves

24 and 38. While the cam 60 is pushing the sides 40 upwards, as viewed in FIG. 5, the fluid in the passageway 99 is compressed locally, that is, within each mold cavity comprising the

semi-cylindrical portions

22 and 42 and to a higher pressure than the compression supplied by the central compression means 11 in the cylinder 10. This final higher compression insures that the molding cavities are filled and that the compression in each molding cavity is the same as that in other cavities and also that the compression in each cavity is the same art molding machines. Since there is no gate hold, the

gate material is not wasted and the gate material need not be broken ofi' the finished article and the surface at the break need not be made smooth. Also, since the portions at 24 and 38 tightly embrace the lead lines 18 throughout the filling, compressing, and hardening process, no fluid leaks out of the mold along the leads 18, whereby more fluid is saved and whereby the leads need not be cleaned. A greatly improved product, at a greater yield, results from the use of the disclosed

molds

20 and 32.

When the top portion 20 of the mold is removed, further movement of the cam 60 to the right ejects the finished encapsulated articles, whereby the pistons 40 not only serve as the lower halves of molding cavities and as parts of open and closeable gates, but also as ejectors.

FIGS. 6 and 7 show another mold in accordance with this invention. In FIGS. 17, similar reference characters have been applied to similar parts. The upper mold portion 20 of FIGS. 1-5 and of FIGS. 6 and 7 are similar. The lower mold portion 100 differs in a manner to be explained.

As shown in FIG. 7, the lower mold portion includes the combs 30, the longitudinal grooves 36, the lead embracing grooves 38, and the raised flat parallelly ex- I fixed portions 102. The top 108 of the pistons 106 is flat and when thejpistons 102 are in their intermediate positions, the flat portions 108 tightly fit against the surface 50 of the upper mold portions 20. At each side of the top portions 108, the pistons 106 are shaped so that in the intermediate positions of the pistons 106 they, with the

cavity portions

22 and 104, form a cylindrical cavity of the shape of the cylindrical portions 16 of the finished article 14. In the lowest positions of the pistons 106 as shown in FIG. 6, a large passageway 99 is provided for fluid flow along the length of the mold comprising the

mold portions

20 and 100 into a first molding cavity, then into a second, and so on to the last cavity. In the top position of the pistons 106, the finished article is ejected from the .open mold. This mold 6f FIGS. 6 and 7 has all the advantages of the mold of FIGS. 1-5. In addition, in the mold of FIGS. 6 and 7, many more cavities may be provided along the length of the mold due to the fact that each piston 106 becomes part of two adjacent cavities whereby the gate distance, the width (as shown in FIGS. 6 and 7) of the flat portion 108, is greatly reduced over the gate distance of FIGS. 105. The pistons 106 are moved up by a cam means such as cam 60 of FIGS. 4 and 5.

- Each time an article is molded by the molds of FIGS. 1-7, the molding fluid is fed into and through the successive molding cavities, whereby the length of passageways for the fluid is minimized, under pressure through wide open gates, whereby the flow of fluid is slow causing no damage to the device to be encapsulated. Then higher pressure is applied to the fluid in the cavities as the pistons 40 in FIGS. 1-5 and 106 of FIGS. 6 and 7 are raised to their intermediate, positions and simultaneously the gates are closed, whereby the passageway is made still shorter and whereby no gate material need be broken off the molded article and whereby the density of the molded article is increased and is made uniform from article to'article and from one portion to another portion of the molded article. Then, after the fluid has hardened and the upper portion 20 of the mold is removed, the

pistons

40 and 106 are raised still further, whereby the finished articles are ejected. v If desired, an article without leads may be molded. In such case, the

surfaces

48 and 50 will be extended flat without

grooves

38 and 24 therein; however, the complementary cavities, which may be given any shape desired, will be retained. Otherwise, no change will be made in the described molds of the several Figures.

What is claimed is: 1. A mold comprising an upper mold portion having a cavity of the shape of a portion of an article to be molded and a flat surface,

. 7 a lower mold portion having spaced parallelly extending flat surfaces adapted to contact said flat surface of said upper mold surface,

said lower mold portions also including spaced fixed bridge poru'ons, I

fixed portions and between said parallel flat surpiston-like moveable parts-positioned between said faces and moveable in directions perpendicular to I said parallelly extending flat surfaces,

said piston-likepart being shaped to fit another por- Q .tionof an article to be molded and an end of said a piston-like portion having a flat'surface adapted to contact said flatsurfaceof said upper mold portions, i said iflat surface positions being spaced from said flat surface of of said piston-like in one of its said uppermold portion for providing a passage for molding fluid into said 'c'avityand in 'another position thereof beingin contact with said flat sur-- face of said upper mold portion for preventing passage of fluid to and from said cavity,

said shaped portionof said piston-likepart insaid other positionforming a continuation of the'surface of a molding cavity, and

' said bridge portions'each being shaped to fit an article and (in said piston-like portion being shaped to fit two articles, one on eachside of said flat end portions. 2. A mold comprising 7 an upper mold portion having a cavity of the shape of a portion of an article to be molded and a flat surface,

a lower mold portion having spaced parallel 1y ex-.

tending flat surfaces adapted to contact said flat surface of said upper mold surface, said lower mold portions also including spaced fixed bridge portions, I piston-like moveable parts positioned between said fixed portions and between said parallel flat surfaces and moveable in directions perpendicular to said upper moldjportion for providing a passage for molding-fluid into said cavity and in another position thereof being in contact with said flat surface of said upper mold portion for preventing passage of fluid to and from said cavity,

said shaped portion of said piston-like part in said other position forming a continuation of surface of a molding cavity, r the ends of said fixed portiom being flat a'nd'lower than said spaced parallelflat surfaces,

an: end of said moveable piston like part having a cavity therein of the shape of another portion of v the article to'be molded and a flat surface which is parallel with said lower flat surfaces, and

the flat surface of said piston-like part szasa ossaas gaszc' sa s? molding fluid.

3. Thein'vention of claim 1 in which said cavities are I each semi-cylindrical and in which said parallelly extending surfaces of said'lower portion extend perpendicular to the axis of said'semi-cylindrical cavities. I

' a s a a r a of said piston-like in one of its being ma a in one position 'thereofto contact the surface of said upper portion and in another position-thereof 1

Claims

1. A mold comprising an upper mold portion having a cavity of the shape of a portion of an article to be molded and a flat surface, a lower mold portion having spaced parallelly extending flat surfaces adapted to contact said flat surface of said upper mold surface, said lower mold portions also including spaced fixed bridge portions, piston-like moveable parts positioned between said fixed portions and between said parallel flat surfaces and moveable in directions perpendicular to said parallelly extending flat surfaces, said piston-like part being shaped to fit another portion of an article to be molded and an end of said piston-like portion having a flat surface adapted to contact said flat surface of said upper mold portions, said flat surface of said piston-like part in one of its positions being spaced from said flat surface of said upper mold portion for providing a passage for molding fluid into said cavity and in another position thereof being in contact with said flat surface of said upper mold portion for preventing passage of fluid to and from said cavity, said shaped portion of said piston-like part in said other position forming a continuation of the surface of a molding cavity, and said bridge portions each being shaped to fit an article and said piston-like portion being shaped to fit two articles, one on each side of said flat end portions.

2. A mold comprising an upper mold portion having a cavity of the shape of a portion of an article to be molded and a flat surface, a lower mold portion having spaced parallelly extending flat surfaces adapted to contact said flat surface of said upper mold surface, said lower mold portions also including spaced fixed bridge portions, piston-like moveable parts positioned between said fixed portions and between said parallel flat surfaces and moveable in directions perpendicular to said parallelly extending flat surfaces, said piston-like part being shaped to fit another portion of an article to be molded and an end of said piston-like portion having a flat surface adapted to contact said flat surface of said upper mold portions, said flat surface of said piston-like part in one of its positions being spaced from said flat surface of said upper mold portion for providing a passage for molding fluid into said cavity and in another position thereof being in contact with said flat surfaCe of said upper mold portion for preventing passage of fluid to and from said cavity, said shaped portion of said piston-like part in said other position forming a continuation of the surface of a molding cavity, the ends of said fixed portions being flat and lower than said spaced parallel flat surfaces, an end of said moveable piston-like part having a cavity therein of the shape of another portion of the article to be molded and a flat surface which is parallel with said lower flat surfaces, and the flat surface of said piston-like part being adapted in one position thereof to contact the surface of said upper portion and in another position thereof to form with said surface of said upper portion and the surface of said fixed portions a passageway for molding fluid.

3. The invention of claim 1 in which said cavities are each semi-cylindrical and in which said parallelly extending surfaces of said lower portion extend perpendicular to the axis of said semi-cylindrical cavities.